How do you determine where to draw the seams or which seams to mark when uv unwrapping a model for texturing?
I’ve looked through several video tutorials but haven’t really, fully understood the logic or theroy behind this decision.
The why and how.
Seam does affect how easily mesh will unwrap with least texture distortion. It helps to place seams away from general view to minimize careful matching of textures between textured faces.
I think the best description is to imagine you’re going to “wallpaper” your object, and you want to find a way to put it on so that there are as few wrinkles in the paper as possible. Marking a seam is like making a cut with a pair of scissors. Sometimes it cuts out a piece entirely, sometimes it makes a single cut, which makes it easier to tuck around a corner.
Obviously, the very easiest thing to do (since a computer does the wallpapering in the end) is to make a small piece of wallpaper for each face. But the other side of the problem is that it’s hard to make two edges of wallpaper blend together. So the fewer pieces of wallpaper you have (or the fewer “rips” in a single piece of wallpaper), the better.
Thus, you are trying to find the balance between two needs: to make the wallpaper (or texture) wrap around the object without too much wrinkling, but also to do it with as few cuts (seams) as you can manage.
I cover how I do this in a video tutorial I did, find it here:
http://vimeo.com/16125012
I use the uv test grid to look for spots where the texture is stretching to help decide where to place seams. Some seams are just common sense, like in my example I place seams around the outside edge of parts of the mesh that are inside the mesh - mouth for example, splitting of the inside of the mouth. Actually I cover quite a bit of stuff on texturing, including hiding the seams I marked, but it is a simple example.
Randy